Field of the Invention
The present invention relates to a motion information acquiring apparatus that acquires motion information from an image, and more particularly to a motion information acquiring apparatus that acquires motion information from time-correlation images.
Description of the Related Art
In the field of acquiring motion information located in an image such as an optical flow, motion information is typically acquired from a difference between two continuously captured images. With such a method, since large motions cannot be accurately acquired, motions on images are reduced by performing high-speed imaging. However, a problem arising when high-speed imaging is performed is that an increase in storage capacity and high-speed processing are needed.
Accordingly, a technique for acquiring motion information only with a single imaging operation by acquiring time-correlation images has been investigated. A time-correlation image is an image representing a time correlation between an image signal obtained by the usual imaging and a predetermined reference signal. Patent Document 1 suggests providing a reference signal with respect to a current obtained by photoelectric conversion and using an image capturing element that integrates the modulated current over time and outputs the integrated current in order to acquire a time-correlation image. However, the image capturing element which is used in this method differs in structure from the typically used image capturing elements, and large design changes are required. Therefore, the production cost rises.
Patent Document 2 suggests a method for acquiring time-correlation images by using a general-purpose image capturing element. As suggested in Patent Document 2, when a single image is acquired, a shutter or light quantity modulating element is controlled according to a reference signal and the incident light quantity is modulated. As a result, time-correlation images representing time correlation with the reference signals can be acquired by using a general-purpose image capturing element. However, with this method, the time-correlation images are acquired with the shutter or light quantity modulating element. Therefore, when correlation with a plurality of reference signals is acquired at the same time, the reference signals need to be changed by time division. The resultant problem is that the sampling number of reference signals decreases. Further, the problem arising when the sampling number is increased is that a plurality of light quantity modulating elements and image capturing elements is needed and the apparatus increases in size.
Patent Document 3 suggests a method in which an object is irradiated with light which has been amplitude modulated at a frequency that differs for each wavelength, and components corresponding to the modulation frequency are extracted in order to implement spectral measurements with the light rays of different wavelengths in a single measurement cycle without using a complex spectrometer. The objective of Patent Document 3 is to acquire spectral information, and the acquisition of time-correlation images for motion information acquisition is not considered.
Patent Document 1: Japanese Patent No. 5441204
Patent Document 2: Japanese Patent Application Publication No. 2013-62582
Patent Document 3: Japanese Patent Application Publication No. 2004-101478